IRJET-Active Power Filter For Power Quality Improvement

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Active Power Filter For Power Quality Improvement Ankit Saxena1, Mr. Gunjan Gupta2 PG (Student), Department of Electronics and Communication Engineering, Invertis University, Bareilly, Uttar Pradesh, India1 Assistant Professor, Department of Electronics and Communication Engineering, Invertis University, Bareilly, Uttar Pradesh, India2

Abstract- This paper tells the contamination issues created

1. Introduction- Increase in such non-linearity

in power systems due to the non-linear features and fast

causes different undesirable features like low system

changing of power electronic equipment. Power quality issues

efficiency and poor power factor. It also causes

are turning stronger because sensitive equipment will be sorer

disturbance to other consumers and interference in

for market competition reasons, equipment will continue

nearby communication networks. The effect of such

contaminating the system more and more due to cost increase

non-linearity may become sizeable over Early

caused by the built-in competition and sometimes for lack of

equipment was designed to withstand disturbances

enforced regulations. Active power filter have been developed

such as lightning, short circuits, and sudden overloads

over the year to solve these problems to improve power

without extra expenditure. Current power electronics

quality. Among which Shunt active power filter (SAPF) is used

(PE) prices would be much higher if the equipment

to control the load current harmonics and reactive power

was designed with the same robustness. Pollution has

compensation. In this work both PI controllers based Fuzzy

been introduced into power systems by nonlinear

Logic checked three-phase SAPF to pay tones and reactive

loads such as transformers and saturated coils;

power by non-linear load to improve power quality is enforced

however, perturbation rate has never reached the

for three-phased three wire systems. Fuzzy controller is based

present levels. Due to its nonlinear characteristics and

on linguistic description and does not require a mathematical

fast switching, PE create most of the pollution issues.

model of the system. A MATLAB program has been formulated

Most of the pollution issues are created due to the

to stimulate the system operation. Various simulation results

nonlinear characteristics and fast switching of PE.

are demonstrated under steady state considerations and

Approximately 10% to 20% of today’s energy is

performance of fuzzy and PI controllers is equated. PWM

processed by PE; the percentage is estimated to reach

pattern generation is based on carrier less hysteresis based

50% to 60% by the year 2010, due mainly to the fast

current control to obtain the

growth of PE capability. A race is currently taking

switching indicates to the

voltage sourced PWM converter.

Keywords- Active power filters, PWM,

place between increasing PE pollution and sensitivity, on the one hand, and the new PE-based corrective harmonics

compensation, power factor correction, power quality. Š 2016, IRJET

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devices, which have the ability to attenuate the issues

voltage source inverter consist of chopping the dc bus voltage

created by PE, on the other hand.

to produce an ac voltage of an arbitrary waveform. There are

the next few years. Hence it is very important to

a large number of PWM techniques available to synthesize

overcome these undesirable features.

sinusoidal patterns or any arbitrary pattern. With PWM

Classically, shunt passive filters, consist of tuned LC

techniques, the ac output of the filter can be controlled as a

filters and/or high passive filters are used to suppress the

current or voltage source device.

harmonics and power capacitors are employed to improve the

Figure 1.2 shows the way PWM works by means of one of the

power factor. But they have the limitations of fixed

simplest and most common techniques: the triangular carrier

compensation, large size and can also exile resonance

technique. It forces the output voltage v over a switching

conditions.

a

cycle, defined by the carrier period of V , to be equal to the

Active power filters are now seen as a viable alternative over the classical passive filters, to compensate

car

average amplitude of the modulating wave V ref. The a

harmonics and reactive power requirement of the non-linear

resulting voltages for a sinusoidal modulation wave contain a

loads. The objective of the active filtering is to solve these

sinusoidal fundamental component V (1) and harmonics of

problems by combining with a much-reduced rating of the

unwanted components. These unwanted components can be

necessary passive components.

minimized using a frequency carrier as high as possible, but

a

this depends on the maximum switching frequency of the Figure 1.1.Voltage source converter topology for active filters

semiconductors (IGBTs, GTOs, or IGCTs).

Most of the active power filter topologies use voltage source converters, which have a voltage source at the dc bus, usually a capacitor, as an energy storage device. This topology, shown in Figure 1.1, converts a dc voltage into an ac voltage by appropriately gating the power semiconductor switches.

Although a single pulse for each half cycle can be applied to synthesize an ac voltage, for most applications requiring dynamic performance, pulse width modulation (PWM) is the most commonly used today. PWM techniques applied to a Š 2016, IRJET

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Figure.1.2. The PWM carrier Technique (triangular carrier).

The modulation strategy shown in Figure 1.3 uses a triangular carrier, which is one of many strategies applied today to control power inverters. Depending on the application (machine drives, PWM rectifiers, or active power filters), some modulation strategies are more suitable than others. The modulation techniques not only allow controlling the inverters as voltage sources but also as current sources. Figure 1.3 shows the compensating current generated for a shunt active

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power filter using three different modulation techniques for

detected from one of the following several symptoms

current-source inverters. These three techniques are periodical

depending on the type of issue involved.

sampling (PS), hysteresis band (HB), and triangular carrier

• Lamp flicker

(TC). The PS method switches the power transistors of the

• Frequent blackouts

active filter during the transitions of a square wave clock of

• Sensitive-equipment frequent dropouts

fixed frequency: the sampling frequency. The HB method

• Voltage to ground in unexpected

switches the transistors when the error exceeds a fixed

• Locations

magnitude: the hysteresis band. The TC method compares the

• Communications interference

output current error with a fixed amplitude and fixed

• Overheated elements and equipment

triangular wave: the triangular carrier. Figure 1.3 shows that

PE

are

the

most

important

cause

of

harmonics,

the HB method is the best for this particular waveform and

interharmonics, notches, and neutral currents. Harmonics are

application because it follows more accurately the current

produced by rectifiers, ASDs, soft starters, electronic ballast for

reference of the filter. When sinusoidal waves are required, the

discharge lamps, switched-mode power supplies, and HVAC

TC method has been demonstrated to be better.

using ASDs. Equipment affected by harmonics includes transformers, motors, cables, interrupters, and capacitors (resonance). Notches are produced mainly by converters, and they principally affect the electronic control devices. Neutral currents are produced by equipment using switched-mode power supplies, such as PCs, printers, photocopiers, and any triplets generator. Neutral currents seriously affect the neutral

Figure.1.3. Current waveforms obtained using different modulation techniques for an active power filter: (a) PS method, (b) HB method, (c) TC method

conductor

temperature

and

transformer

capability.

Interharmonics are produced by static frequency converters, cyclo-converters, induction motors & arcing devices.

Equipment presents different levels of sensitivity to PQ

1.1 Power Quality- The PQ issue is defined as “any

issues, depending on the type of both the equipment and the disturbance. Furthermore, the effect on the PQ of electric

occurrence manifested in voltage, current, or frequency

power systems, due to the presence of PE, depends on the type

deviations that results in damage, upset, failure, or mis-

of PE utilized. The maximum acceptable values of harmonic

operation of end-use equipment.” Almost all PQ issues are

contamination are specified in IEEE standard in terms of total

closely related with PE in almost every aspect of commercial,

harmonic distortion.

domestic, and industrial application. Equipment using power

Power electronics are alive and well in useful applications to

electronic devise are residential appliances like TVs, PCs etc.

overcome distribution system problems. Power electronics has

business and office equipment like copiers, printers etc.

three faces in power distribution: one that introduces valuable

industrial equipment like programmable logic controllers

industrial and domestic equipment; a second one that creates

(PLCs), adjustable speed drives (ASDs), rectifiers, inverters,

problems; and, finally, a third one that helps to solve those

CNC tools and so on. The Power Quality (PQ) problem can be © 2016, IRJET

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On

one

hand,

power

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and

nonlinear loads or supply lines, respectively. Different active

microelectronics have become two technologies that have

power filters topologies have been introduced and many of

considerably improved the quality of modern life, allowing the

them are already available in the market.

introduction of sophisticated energy-efficient controllable

2. Shunt Active Power Filter- The shunt-connected

equipment to industry and home. On another hand, those same

active power filter, with a self-controlled dc bus, has a

sensitive technologies are conflicting with each other and

topology similar to that of a static compensator (STATCOM)

increasingly challenging the maintenance of quality of service

used for reactive power compensation in power transmission

in electric energy delivery, while at the same time costing

systems. Shunt active power filters compensate load current

billions of dollars in lost customer productivity.

harmonics

by

injecting

equal-but

opposite

harmonic

compensating current. In this case the shunt active power

1.2 Solutions to Power Quality Problems- There are two approaches to the mitigation of power quality

filter operates as a current source injecting the harmonic components generated by the load but phase-shifted by 180°.

problems. The first approach is called load conditioning, which ensures that the equipment is made less sensitive to power disturbances, allowing the operation even under significant voltage distortion. The other solution is to install lineconditioning systems that suppress or counteract the power system disturbances. Passive filters have been most commonly used to limit the flow of harmonic currents in distribution systems. They are usually custom designed for the application.

However, their performance is limited to a few harmonics, and they can introduce resonance in the power system. Among the

Figure.2.1 Shunt active power filter topology.

different new technical options available to improve power quality, active power filters have proved to be an important and flexible alternative to compensate for current and voltage disturbances in power distribution systems. The idea of active filters is relatively old, but their practical development was made possible with the new improvements in power electronics and microcomputer control strategies as well as with cost reduction in electronic components. Active power filters are becoming a viable alternative to passive filters and are gaining market share speedily as their cost becomes competitive with the passive variety. Through power

Figure 2.2 Filter current IF generated to compensate load-

electronics, the active filter introduces current or voltage

current harmonics

components, which cancel the harmonic components of the Š 2016, IRJET

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Figure 2.1 shows the connection of a shunt active power filter

PWM current controller to generate switching signals of the

and Figure 2.2 shows how the active filter works to

PWM converter[2]. The difference of reference current

compensate the load harmonic currents.

template and actual current decides the operation of switches.

To increase current of particular phase, the lower switch of the

2.1 PI Control Scheme- The complete schematic

PWM converter of that particular phase is switched on, while

diagram of the shunt active power filter is shown in figure

to decrease the current the upper switch of the particular

2.1.1. While figure 2.1.2.gives the control scheme realization.

phase is switched on. These switching signals after proper

The actual capacitor voltage is compared with a set reference

isolation and amplification are given to the switching devices.

value.

Due to these switching actions current flows through the filter inductor L , to compensate the harmonic current and reactive c

power of the load, so that only active power drawn from the source.

2.2 Fuzzy Control Scheme- Fig.2.2.1 shows the block diagram of the implemented fuzzy logic control scheme of a shunt active power filter. Fig.2.2.2 shows the schematic diagram of the control algorithm. In order to implement the control algorithm of a shunt active power filter in closed loop, Figure 2.1.1 Schematic diagram of shunt active filter.

thee DC side capacitor voltage is sensed and then compared with a reference value. The obtained error e (=V

dc,ref

-V

dc,act

) and

the change of error signal ce(n)=e(n)-e(n-1) at the nth sampling instant as inputs for the fuzzy processing. The output of the fuzzy controller after a limit is considered as the amplitude of the reference current I

max

takes care of the active

power demand of load and the losses in the system.

Figure .2.1.2 APF Control scheme with PI controller.

The error signal is fed to PI controller. The output of PI controller has been considered as peak value of the reference current. It is further multiplied by the unit sine vectors (u , u , sa

sb

and u ) in phase with the source voltages to obtain the sc

*

*

*

reference currents (i , i , and i ). These reference currents sa

sb

sc

and actual currents are given to a hysteresis based, carrierless Š 2016, IRJET

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a nonlinear load, a voltage source PWM converter, and a fuzzy controller or a PI controller. All these components are modeled separately, integrated and then solved to simulate the system.

Figures 3.1-3.3 show the simulations results of the proposed shunt active power filter controlled by fuzzy logic and a conventional PI controller with MATLAB program. The parameters selected for simulation studies are given in table 3.1. The three phase source voltages are assumed to be balanced and sinusoidal. The source voltage waveform of the reference phase only (phase-a, in this case) is shown in fig.3.1.

A load with highly nonlinear characteristics is considered for Figure2.2.1.Schematic diagram of closed loop fuzzy logic controlled shunt active power filter

the load compensation. The THD in the load current is 22.05%.

The phase-a load current is shown in figure 3.2. The source current is equal to the load current when the compensator is

The switching signals for the PWM converter are obtained by comparing the actual source currents (i , i , and i ) with the

not connected.

System Parameters

Values

Source voltage (Vs)

100V (peak)

System frequency (f)

50 Hz

amplification and isolation, are given to switching devices of

Source impedance

0.015ohm;0.12mH

the PWM converter [6].

(Rs,Ls)

sa

*

*

sb

sc

*

reference current templates (i , i , and i ) in the hysteresis sa

sb

sc

current controller. Switching signals so obtained, after proper

Filter Impedance (Rc,Lc)

0.32ohm;2.8mH

Load impedance (Rl,Ll)

5.3ohm;17.5mH

DC Link capacitance

2000uF

Reference DC link

220V

voltage (Vdcref) Table3.1.System parameters for simulation study.

Figure2.2.2.Fuzzy Control scheme

3. Simulation Result- A program is developed to simulate the both PI controller based and fuzzy logic based shunt active power filter in MATLAB. The complete active power filter system is composed mainly of three-phase source, Š 2016, IRJET

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From the responses it is depicted that the settling time required by the PI controller is approximately 10 cycles whereas in case of fuzzy controller is about 7.5 cycles. The peak overshoot voltage incase of PI controller is 880Volts (approx) whereas in case of fuzzy controller is 780volts (approx). The source current THD is reduced form 22.05% to 2.58% which is below IEEE standard with both the controllers.

After compensation both source voltage and current are in phase with each other means that the harmonics are eliminated and reactive power is compensated to make power factor close to unity. As the source current is becoming

Fig.3.1 Result-1

sinusoidal after compensation power quality is improved.

4. Conclusions- A shunt active power filter has been investigated

for

power

quality

improvement.

Various

simulations are carried out to analyze the performance of the system. Both PI controller based and fuzzy logic controller based Shunt active power filter are implemented for harmonic and reactive power compensation of the non-linear load. A program has been developed to simulate the fuzzy logic based and PI controller based shunt active power filter in MATLAB. It is found from simulation results that shunt active power filter

Fig.3.2 Result-2

improves power quality of the power system by eliminating harmonics and reactive current of the load current, which makes the load current sinusoidal and in phase with the source voltage. The performance of both the controllers has been studied and compared. A model has been developed in MATLAB SIMULINK and simulated to verify the results. The fuzzy controller based shunt active power filter has a comparable performance to the PI controller in steady state except that settling time is very less in case of fuzzy controller.

The THD of the source current is below 5%, the harmonics limit imposed by IEEE standard.

Fig.3.3 Result-3

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